Old Fortress Corfu ...

... seen from near our van stop, early this morning.  The earliest signs of fortifications date from the 6th century. In the 15th C the Venetians built a moat (the Contrafossa) which created an artificial island. The citadel came under repeated attach by the Ottomans  in 1537, 1571 and 1716.  (The Wiki article is helpful.)